1
Preparation and Characterization of novel PSf/PVP/PANI-nanofiber
Nanocomposite Hollow fiber Ultrafiltration Membranes and their
possible applications for Hazardous Dye rejection
Avin J. Kajekara, B.M. Dodamani
a, Arun M. Isloor
b,*, Zulhairun Abdul Karim
c, Ng Be
Cheerc, A. F. Ismail
c and Simon J. Shilton
d
a Department of Applied Mechanics and Hydraulics, National Institute of Technology
Karnataka, Surathkal, Mangalore 575 025, India. bAdvanced Membrane TEchnology Research Centre (AMTEC), Universiti Teknologi
Malaysia, 81310 UTM, Skudai, Johor, Malaysia. cMembrane Technology Laboratory, Department of Chemistry, National Institute of
Technology Karnataka, Surathkal, Mangalore 575 025, India. dDepartment of Chemical and Process Engineering, University of Strathclyde, James
Weir Building, 75 Montrose Street, Glasgow, G1 1XJ, Scotland
Abstract
In the present study, PANI (Polyaniline)-nanofibers were synthesized by interfacial
polymerization technique, dispersed in n-Methyl-2-Pyrrolidone (NMP) solvent and blended
with PVP (Polyvinylpyrrolidone)/PSf (Polysulfone) for preparing the novel hollow fiber
membrane by dry-wet spinning technique. The newly prepared nanocomposite ultrafiltration
hollow fiber membrane is characterized by Scanning Electron Microscope (SEM), Contact
Angle, Zeta Potential and Differential Scanning Calorimeter (DSC). Filtration studies are
conducted to measure the membrane Pure Water Flux (PWF), rejection of Hazardous Dye
(Reactive Red 120) and Fouling Resistance. The maximum rejections are obtained for M 0.5
membrane with 99.25 % rejection of RR120 hazardous dye at 2 bar pressure. The pure water
flux, percentage rejection, antifouling property and thermal resistance increased with increase
in PANI-nanofiber concentration. The contact angle of the membrane decreased with
increasing PANI-nanofiber concentration, which indicated increased hydrophilicity of the
new membranes.
Keywords: Hollow fiber membrane, Ultrafiltration, PANI-nanofiber, Dye rejection
*Corresponding author: [email protected], Tel: +91 9448523990
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1. Introduction
Water is the most important resource on this planet. It is the basic necessity for survival
of all living organisms and is used in agriculture and most of the industries. Among the
chemical industries, dye industry is also one among them. Dye and its intermediates are used
in textile, printing inks, paper, plastics, paint and food industries to add color and patterns [1].
Nowadays, natural dyes are being replaced by synthetic chemical dyes, as they are more
economical, have brighter colours, good retaining capacity and are easy to apply on the
fabrics. There are more than 100,000 commercial dyes and their total consumption in the
worldwide textile industry is more than 10,000 tonnes/year and this in turn discharges more
than 100 tonnes/year of dyes into waste streams [2]. The water used for processing dyes,
rinsing textiles and cleaning the processing equipment become highly contaminated and their
discharge inturn pollutes the surface and ground water. Dyes have complex aromatic
molecular structure and because of their synthetic origin, they are very stable to temperature,
oxidizing agents and bio-degradation. Thus, they are a grave threat to human, animal and
aquatic life due to their non-degradable nature, undesirable color, toxic and carcinogenic by-
products and their capacity to increase Chemical oxygen demand (COD) levels of water
sources [1].
Various methods such as, adsorption [2-3], flocculation-coagulation [4], advanced
oxidation processes [5-6] and membrane separation [7-14] have been developed and adapted
for removal of the dye and its intermediates from the contaminated water. Membrane
filtration technologies are considered as one of the most effective for removal of
contaminants from water due to their high efficiency, selective removal, easy operation and
small footprint. Some of the membrane processes used are, reverse osmosis (RO),
nanofiltration (NF), ultrafiltration (UF), membrane electrolysis and membrane bio-reactor
(MBR).
Ong et al. [7] have evaluated the performance of membranes under various operating
conditions for both lab-scale as well as pilot-scale and reported very robust performance with
more than 90% rejection for various dyes. Yu et al. [8] and Wei et al. [9] have used thin-film
composite hollow fiber nanofiltration for successful removal of dyes from aqueous solutions
with maximum rejections of greater than 99%. Zheng and team [10] prepared positively
3
charged thin-film composite hollow fiber nanofiltration membranes and observed rejections
of 99.8%, 99.8% and 99.2% for Brilliant Green, Victoria Blue B and Crystal Violet
respectively using the submerged filtration technique. Maurya et al. [11] successfully used
Polysulfone-Polyvinlypyrrolidone ultrafiltration hollow fiber membranes for treatment of
aqueous dye solutions such as Rhodamine B and Reactive Black-5 and observed a maximum
dye rejection of 97% along with a maximum flux of 35 L.m-2
.h-1
. Afonso and Borquez [12]
have adopted the ultrafiltration technique for treatment of seafood processing wastewaters
and have shown that UF can be a promising technique for recovery of valuable proteins.
Hamid et al. [13] have prepared PSf/TiO2 hollow fiber ultrafiltration membranes for the
removal of humic acid and achieved rejection greater than 91% along with less fouling
sensitivity to humic acid deposition. Yuliwati et al. [14] used PVDF based hollow fiber
ultrafiltration membranes for treatment of refinery wastewater and reported flux of 82.5
L.m-2
.h-1
and maximum rejection of 98.8%.
Ultrafiltration is a well-established membrane technique and has been used for many
applications. Ultrafiltration requires much lesser energy than nanofiltration and or reverse
osmosis.. Ultrafiltration separation based on size exclusion or particle capture. Ultrafiltration
can be applied in either cross-flow or dead-end mode. Adapting the cross-flow mode for dye
removal from aqueous medium in addition to higher resistance to scale formation, has an
added advantage that, it separates out the raw wastewater into purified water and a dye
concentrate stream. This concentrate stream can be further processed to recycle and reuse
salts and dyes and thus mitigate environmental pollution. In membrane based treatment of
dye wastewater, there are multiple retentate streams which can be reused within the dyeing
industry. Recovery of water and sodium chloride up to 99 % has been reported by Allègre et
al. [15] [16]. The recovered water and salts have been successfully reused within the dyeing
industry. Few other case studies [17] also report recovery of either water or added salts for
reuse in the dye industries.
Recovery of dyes from wastewater are usually more difficult as most dyeing operations
use many different colors and it may not be feasible to separate individual dyes to reuse. A
textile plant in Liberty, South Carolina has reported a method of recovering indigo dye from
the rinse water since 1981 [18]. Typically the process needs to be isolated before adding other
dyes and an ultrafilter is used to recover the indigo dye at the process where it is generated.
This has yielded considerable cost savings from recovering the expense indigo dye and the
cost for the dye recovery system was recovered before the end of its second year of operation
[18]. It is reported that a project sponsored by the Environmental Protection Agency (EPA)
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has also set up a process for reclamation and reuse of hot rinse water and neural, anionic and
cationic dyes [19].
Polysulfone (PSf) membranes have high mechanical strength along with good thermal
and chemical resistance and hence have been widely used for many applications. It is widely
available, inexpensive, easy to process and very stable. However, its hydrophobic nature
reduces its water flux and fouling resistance, which lessens its applications for water
filtration. Hence various techniques have been used to improve its porosity and surface
hydrophilicity like, grafting, polymer blending, coating and irradiation [20]. Polymer
blending technique for hydrophilic surface modification is one of the preferred options due to
its good performance, easy operation and stability of the product. Isloor and co workers
prepared novel PSf membranes for various applications using different additives like chitosan
and its derivatives [21-22], poly-amides [23], TiO2 nanotubes [24] etc., and have seen
increased performance and fouling resistance.
Nanocomposite membranes have gained a lot of interest due to the significant
improvement of membrane permeability, increased flux, hydrophilicity and antifouling
property [25]. Nanomaterials like TiO2 nanoparticles, Al2O3 nanoparticles, single and
multiwalled Carbon nanotubes, have been successfully blended with polymer materials to
produce membranes having varied and unique properties. Razmjou et al. [26] studied
performance of polyethersulfone nanocomposite membranes by incorporating TiO2
nanoparticles and have observed enhancement in pure water flux, higher thermal resistance
and larger pore size. Nanofiber incorporated membranes are expected to remove particles
from the aqueous phase at a high rejection rate without significant fouling and have been
proposed to be used for pre-treatment for reverse osmosis [25]. Nanocomposite membranes
are observed to have increased membrane surface hydrophilicty, water permeability and
fouling resistance. Antimicrobial nanomaterials such as nano-Ag and Carbon nano tubes
(CNT) have been incorporated to inhibit biofilm formation. Jeong et al. [27] prepared thin
film nanocomposite membranes for reverse osmosis application using zeolite nanoparticles
dispersed within polyamide films and has reported increased permeability with higher zeolite
nanoparticle loading where rejection was in excess of 90% at the 50% recovery and was
comparable to commercial RO membranes.
Polyaniline (PANI) is an organic conducting polymer, which has been used for a wide
variety of applications. It is also very easy to synthesize and has good environmental stability.
It has been used in ultrafiltration membranes, proton exchange membranes, gas separation
and pervaporation membranes for many applications. PANI nanomaterials have been
5
synthesized in various morphologies like nanoparticle, nanotube, nanoflake and nanofiber
and used in polymer blends [28]. Some of the different methods used to fabricate PANI-
nanofibers are hard and soft templates, interfacial polymerization, seeding, rapid mixing and
electrospinning. PANI-nanofiber exhibits varied properties when compared to bulk PANI,
which has increased surface area and better processibility [29]. Better processibilty relates to
better dispersion and easier bonding during membrane formation. Polymer nanofibrous
membranes are also reported to have many attractive attributes to increase membrane
permeability [30]. Fan et al. [30] have shown that, the addition of PANI-nanofibers have
resulted in improved membrane performance due to increased porosity and interconnected
pores within the membrane structure.
Polyvinylpyrrolidone (PVP) is a water-soluble polymer and has been used as a pore-
forming agent for membranes. Chakrabarty et al. [31] demonstrated that, the addition of PVP
to membrane casting solutions results in the increase of membrane porosity as well as
increase in the number of pores.
Hollow fiber membranes have been used in several commercial applications such as
bio-separations, water purification, wastewater treatment and gas separations due to their
excellent mass-transfer properties. Hollow fiber membranes have higher surface area per unit
of membrane module volume and hence increased water flux [7]. For preparation of the
hollow fiber membranes, the parameters during spinning are very important and these are to
be carefully controlled to prepare membranes of required characteristics for specific
applications. Some of these parameters are the type of polymers, solvents used, additives
added to the polymer dope, the rate of extrusion of dope solution and bore fluid, type of bore
fluid, the air gap distance, and the type of coagulant and coagulant bath temperature [32].
In view of the above observations and in order to enhance the membrane properties, it
was planned to combine the properties of these individual components. In the present study,
PANI-nanofibers were synthesized by interfacial polymerization technique wherein the
polymerization reaction takes place at the interface of the two immiscible liquids. The PANI-
nanofibers are then dispersed in n-Methyl-2-Pyrrolidone (NMP) solvent and then blended
with PVP and PSf for preparing the novel hollow fiber membranes by dry-wet spinning
technique. The newly prepared nanocomposite ultrafiltration hollow fiber membrane is then
characterized by Scanning Electron Microscope (SEM), Contact Angle, Zeta Potential and
Differential Scanning Calorimeter (DSC). Filtration studies are conducted to measure the
membrane Pure Water Flux (PWF), rejection of hazardous dye (Reactive Red 120) and flux
recovery for the membranes. To the best of our knowledge this is the first study on the effect
6
of PANI-nanofibers on hollow fiber ultrafiltration membranes and their possible applications
for rejection of Reactive Red 120 dye from water.
2. Materials and Methods
2.1 Materials
Udel® P-1700 Polysulfone (PSf) pellets were obtained from Solvay company. Aniline was
purchased from AnalaR Normapur®. 1N Hydrochloric Acid (HCl), n-Methyl-2-Pyrrolidone
(NMP) and Ammonium Persulfate (APS) was purchased from Merck. Polyvinylpyrrolidone
(PVP) and Reactive Red 120 (RR120) dye were procured from Sigma-Aldrich. The
Molecular structure of RR120 is shown in Fig.1. O-Xylene was purchased from S.D Fine-
Chem Ltd. Aniline was distilled under vacuum before usage and all other chemicals were
used as received.
Fig.1: Molecular structure of Reactive Red 120 dye.
2.2 Synthesis of PANI-nanofibers
PANI-nanofibers were synthesized by interfacial polymerization of aniline as reported in
literature [33]. The molar ratio of Aniline to APSwas kept at 1:1. Thus, 2g of Aniline was
dissolved in 2ml of o-Xylene and 4.674g of APS was dissolved in 98ml of 1N HCl by
stirring. The aniline solution was added slowly to the APS solution with vigorous stirring.
The reaction is allowed to continue for 120 minutes and the blue-green PANI-nanofiber
precipitate was collected. The precipitated product is then washed with deionized water and
methanol continuously and separated by centrifuging. The PANI-nanofiber product is then
dried in oven for 48 hours and ground into a fine powder using mortar and pestle.
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2.3Preparation of PSf/PVP/PANI-nanofiber dopes
The polymer solution used for spinning hollow fiber membrane is termed as ‘dope’. PANI-
nanofibers in various concentrations are added to NMP solvent and sonicated for 30 minutes
for effective dispersion. After this, PVP and PSf are dissolved in NMP under heating and
continuous stirring for 48 hours until a homogeneous solution is formed. For all the prepared
solutions, mass ratio of PSf to total solution was 15 weight% and PVP was 2 weight% of PSf.
The PANI-nanofiber concentrationvaried between 0 – 1.0 weight% of PSf and the rest was
made up with NMP as detailed in Table1.
Table1: Dope solutions for PSf/PVP/PANI Nanofiber hollow fiber membrane
PSf (g) PVP (g) PANI-nf (g) NMP (g)
M0 18 0.36 0.0 81.64
M1 18 0.36 0.045 81.60
M2 18 0.36 0.090 81.55
M3 18 0.36 0.180 81.46
2.4 Preparation of PSf/PVP/PANI-nanofiber hollow fiber membranes
The novel membrane is spun by dry-wet spinning method at room temperature by hollow
fiber spinning machine as shown in Fig.2.
Fig.2: (a) Schematic representation of the hollow fiber spinning set up, (b) cross-section of
the spinneret during spinning [24].
The polymer dope solution was pressurized through a spinneret by controlling the extrusion
rate. The spinneret was placed at a fixed distance above the water bath for the dry-wet
process. Distilled water was used as a bore fluid to create the hollow fiber. The hollow fiber
that emerged from the tip of the spinneret was guided through the two water baths and
carefully adjusted to match the free falling velocity. The fibers were then finally guided to a
8
collection drum after the solidification process. The detailed spinning parameters are listed in
Table 2.
Table 2: Spinning Parameters for PSf/PVP/PANI-nanofiber hollow fiber membranes
Parameter Value
Dope Extrusion Rate 2.5 ml/min
Bore Fluid Distilled Water
Bore Fluid Rate 0.833 ml/min
Collection Drum Rate 9.4 m/min
Air gap distance 5 mm
Spinneret o.d/i.d 0.3/0.6 mm
2.5 Post-Treatment of PSf/PVP/PANI-nanofiber membranes
The newly spun hollow fibers were immersed in distilled water bath for 3 days, with daily
change of the water to remove residual solvent. The hollow fibers were then post-treated with
10 wt.% glycerol aqueous solution as a non-solvent exchange for 1 day to minimize fiber
shrinkage and pore collapse [14]. Finally the treated fibers were dried for 3 days and then
they were used to prepare hollow fiber test modules.
2.6 Membrane Characterization
2.6.1 Morphology of the membrane
The surface and cross section morphologies of the membrane were studied using a table top
Scanning Electron Microscope (SEM) (Model: TM 3000, Hitachi). The hollow fiber
membranes were immersed in liquid nitrogen and fractured to obtain its cross section. All
samples were gold sputtered under vacuum before the SEM measurements.
2.6.2 Membrane Contact Angle
To evaluate the membrane surface hydrophilicity, the static contact angle was measured by
sessile drop method using contact angle goniometer (Model: OCA 15EC, Dataphysics) [34].
At least twenty water contact angles at different locations on membrane surface were
averaged and reported.
2.6.2 Zeta Potential measurements
Zeta Potential was calculated after measuring the streaming potentials of the hollow fiber
membranes. To study the nature of membrane surface charge between pH ranges of 2.0-7.0, a
multi-point testing approach was adopted using a SurPASS electrokinetic analyser (Anton
Paar, Graz, Austria). For the analysis, potassium chloride (1mM) was used as electrolyte and
9
0.1M Hydrochloric acid and 0.1M sodium hydroxide were used as titration solutions. All
Zeta Potential calculations were the average of four measurements at the same pH.
2.6.3 Differential Scanning Calorimetry studies
Differential Scanning Calorimetry studies help us to measure the glass transition temperature
(Tg) of the membranes. Tg is a measure of the degree of rigidity of the polymer chain. The
procedure for the testing was adopted as per reported literature [35]. (Model: Mettler Toledo
DSC 822e). The membrane samples were weighed and heated between a temperature range
of 30 - 400°C at a heating rate of 10
°C min
-1 to remove the thermal history and were cooled
thereafter from 400°C - 30
°C at a cooling rate of 10
°C min
-1. The heating cycle was then
repeated as earlier and Tg of the sample was determined.
2.7 Filtration Studies
2.7.1 Pure Water Flux (PWF) studies
Filtration experiments were performed using self fabricated cross-flow filtration cell as
shown in Fig.3. Membrane modules were prepared by ‘potting’ the ends of a stainless steel
pipe with epoxy adhesive and hardener. Each membrane module comprised of 10 hollow
fibers of 20 cm length.Membranes were initially compacted at trans-membrane pressure
(TMP) of 2 bar for 30 minutes before proceeding with the flux measurements. PWF was
calculated using the following equation,
Where, (L.m-2
.h-1
) is the pure water flux, and (L) is the amount of water collected for
(h) time duration using a membrane of area (m2).
a
b
c
d
e f
Permeate
Retentate
Feed
10
Fig.3: Self-Fabricated cross-flow filtration setup (a) Feed tank, (b) Diaphragm pump (c)
Bypass valve (d) Pressure Guage (e) Membrane module (f) Retentate Flow-control valve
2.7.2 Hazardous Dye rejection studies
The dye rejection performances of all hollow fiber membranes were studied using the cross-
flow filtration setup. 300 ppm of RR120 dye in aqueous solution was used as feed. The
rejection studies were conducted at a constant pressure of 2 bar and permeate was collected
for a known interval of time. The absorbance of RR120 dye was measured at 535 nm
wavelength with a Hitachi U5000 spectrophotometer. Then the percentage rejection was
calculated using the following equation,
where, = rejection (%), and are the concentrations (mM) of permeate and feed
solutions, respectively.
Since concentration is directly proportional to the measured absorbance, we can also
calculate rejection using the following equation,
where, = Rejection (%), and are the Absorbance values of permeate and feed
solutions, respectively.
2.7.3 Antifouling studies
To evaluate the antifouling property of the membrane, after dye filtration for 60 minutes, the
membrane was subjected to pressurized cleaning with pure water atincreased pressure of 4
bar for 10 minutes and then the flux of the membrane , was measured according to the
method described earlier in section 2.7.1 at a pressure of 2 bar. The flux recovery ratio was
calculated using the following equation,
Where, is flux recovery ratio (%), and are the pure water flux (L.m-2
.h-1
) and flux
after cleaning (L.m-2
.h-1
) of the membrane, respectively.
3. Results and Discussion
3.1 Synthesis of PANI-nanofibers
11
PANI-nanofibers were synthesized by interfacial polymerization of aniline monomer in
acidic medium. Standard chemical oxidation polymerization of aniline yields agglomerated
PANI without nanofiber morphology. In the interfacial polymerization technique, the
polymerization reaction takes place at the interface of the two immiscible liquids [28]. The
vigorous stirring results in the dispersion of o-xylene as micro droplets increasing the area
available for interfacial polymerization. Nanofiber size and yield was affected by the mole
ratio of oxidant to aniline [33]. As observed in SEM and TEM images and shown in Fig.4,
the PANI-nanofiber diameters were in the range of 60 – 80 nm and length was around 150 –
300 nm. PANI-nanofibers are hydrophilic in nature and hence increase the membrane
wettability and subsequently the water flux when blending with polymer membranes [30].
Fig. 4. TEM images of PANI coated TiO2 nanotubes (A and B)
3.2 Membrane Morphology
The addition of PVP and PANI-nanofibers greatly increased the viscosity of the casting dope
solution. The addition of PVP may have resulted in reduced interaction between PSf and
NMP thereby reducing the solvating power of NMP [36]. Also, the increase in viscosity due
to the addition of PANI-nanofibers may be due to its large chain dimension, which was easy
to aggregate and its ability to gather NMP due to the high surface energy, which weakened
PSf and NMP interaction [36]. Thus, when increase of PANI-nanofiber concentration to 1.0
wt% of PSf, it was difficult to disperse them evenly in the casting dope solution and it
clogged the spinneret during the hollow fiber spinning process.
From the SEM images of the membrane surface shown in Fig.5, it is observed that,
the membrane is having morphology with asymmetric pores and non-uniform distribution of
pores. The cross section image showed that, the membranes have well formed asymmetrical
12
structure with dense top layers and porous sub-layer. There were well-formed finger like
pores of almost equal length, with interconnected macrovoids below both outer and inner
surfaces demarked by a thin polymer layer. PANI-nanofibers have high surface energy and
hydrophilicity, thus when the hollow fiber membrane was immersed in a water bath, the
PANI-nanofibers may migrate from the polymer matrix towards the water bath so as to
reduce the interfacial energy between the two phases [30]. The migration would leave
cavities in the polymer matrix, which in turn would increase the membrane porosity and have
interconnection between the finger like pores and macrovoids. This agrees with research of
Fan et al. [30], who reported higher membrane porosity and better interconnected pores in
PSf/PANI-nanocomposite membrane compared to the neat PSf membrane. The PANI-
nanofibers aggregate on the polymer-water interface skin layer leading to the dense top layer
morphology and increases the membrane surface hydrophilicity. The membrane had a
porous internal structure, which may be due to the addition of PVP in the polymer dope. PVP
is a water-soluble polymer and hence most of it may be leached out from the polymer matrix
when the membrane is immersed into water bath and these sites become micro pores [36].
Also, there is an increase in the number of pores on the membrane surface due to PVP
additive. The increase in pores may be due to increased viscosity of the casting solution and a
reduction in the miscibility of the casting solution with water, which may increase the ratio of
water inflow to solvent outflow resulting in a more porous membrane [31] [36].
Simultaneously, there is also a reduction in the size of the pores due to additives. The higher
molecular weight additives may take longer time to reach the membrane surface during the
membrane formation process which will give sufficient time for the polymer molecules to
aggregate on top of it and form a denser skin layer with the relatively smaller size pores [31].
However, Fan et al. [30] have reported a slight increase in the pore size due to the addition of
PANI-nanofibers. Zhao et al. [36] found that, addition of PVP and PANI-nanofibers
decreased the thermodynamic stability of the casting solution thus enhancing demixing of the
casting solution. It was also reported that, there was a decrease of water intake during
preparation leading to improvement in membrane structure and performance.
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Fig.5: SEM images of PSf/PVP/PANI-nanofiber hollow fiber membrane cross-sections. (a,
A) Sample-00: M0, (b,B) Sample-01: M0.25, (c,C) Sample-02: M0.5.
3.2 Contact Angle
14
Contact Angle is a good indication of hydrophilic property of the material. The static contact
angles for the new membranes measured by the sessile drop method are reported in Fig.6.
From the figure it is clear that, the contact angle reduces with increasing concentration of
PANI-nanofiber indicating an increase in the hydrophilicity of the membrane. As discussed
in section 3.2, this may be due to PANI-nanofibers, which migrate towards the polymer-water
interface and aggregate at the membrane surface [36]. The PANI-nanofibers being highly
hydrophilic in nature may be responsible for reducing the water contact angle on the
membrane surface.
Fig.6: Contact angle measurements of PSf/PVP/PANI-nanofiber hollow fiber membranes.
3.3Zeta Potential measurements
The different ionisable groups in the membrane material affect the zeta potential values of the
membrane for range of pH. Zeta potentials calculated based on measurements of streaming
potential of the hollow fiber membranes between pH ranges of 2.0-7.0 are shown in Fig.7.
The pH dependent measurements enable us to identify the isoelectric point of the membranes
[37]. The isoelectric point is the pH value when there is no charge present on the membrane
surface. From the graph, we can observe that the isoelectric point of the membranes shift
towards lower pH with increasing PANI-nanofiber concentration and that the membrane
surface has a negative charge over almost the entire pH range tested. This is a qualitative
indicator of electrostatic contribution to the rejection of dyes [20].
85
86
87
88
89
90
91
92
93
94
M0.0 M0.25 M0.5
Con
tact
An
gle
(D
egre
es)
Membranes
Contact Angle Measurements
15
Fig.7: Zeta Potential measurements of PSf/PVP/PANI-nanofiber hollow fiber membranes.
3.4 Differential Scanning Calorimetry (DSC) studies
DSC graphs for the new membranes are shown in Fig.8. The glass transition temperature (Tg)
of the membranes increase with increasing concentration of PANI-nanofibers and thus have
higher thermal resistance [38]. Usually the dyeing and rinsing procedures on textiles are
conducted at temperatures higher than room temperature and hence higher temperature
wastewater is generated [7] [35]. Thus one can conclude that, the membrane has better
resistance for treating higher temperature dye wastewater.
Fig.8: DSC thermographs of PSf/PVP/PANI-nanofiber hollow fiber membranes.
3.5 Pure Water Flux (PWF) Studies
-25
-20
-15
-10
-5
0
5
1 2 3 4 5 6 7 Z
eta P
ote
nti
al
FM
(m
V)
pH
Zeta Potential Measurements
M0
M0.25
M0.5
256.88oC 204.6oC
172.79oC
297.66oC
-4
-2
0
2
4
6
8
10
12
0 100 200 300 400
DS
C V
alu
e (m
W)
Temperature , Ts (oC)
DSC Measurements
M0.5
M0.25
M0
16
Hollow fiber membranes show increased water flux when compared to flat sheet
membranes since they have a higher surface area per unit of membrane module volume. The
membrane cross-flow filtration tests indicate that, flux increases with increasing PANI-
nanofiber concentration for constant pressure of 2 bar as shown in Fig.9. The higher water
flux for new membranes can be attributed to increased hydrophilicity and increased porosity
due to PVP and PANI-nanofiber additives. The nanocomposite membrane showed increased
flux and rejection due to the additives. The PANI-nanofibers are hydrophilic in nature and
during the membrane formation process, they migrate towards the surface of the membrane
[30]. This migration through the polymer matrix, forms finger like interconnected pores in
the membrane cross section. This increases flux and reduces resistance to flow of water
through the membrane Also, due to the hydrophilic PANI-nanofibers moving to the surface,
the membrane surface becomes more hydrophilic and this in turn increases wetting of the
surface contributing to the increase in flux. PVP has been used as a pore forming agent and is
reported to increase the formation of pores on the membrane surface [31] thus increasing flux
of water through the membrane. Also, since PVP is a water-soluble polymer, it may be
leached out from the polymer matrix when the membrane is immersed in water, causing the
formation of micro voids and thereby increasing the porosity of the membrane [36].
Fig.9: PWF of PSf/PVP/PANI nanofiber hollow fiber membrane.
3.6 Hazardous Dye rejection and Flux Recovery Studies
The new membranes showed very good rejection for RR120 dye at 2 bar pressure. The %
rejection of dyeincreases with increase in PANI-nanofiber concentration as shown in Fig.10
0
10
20
30
40
50
60
70
10 20 30 40 50 60 70 80
PW
F, J
W (
L.m
-2.h
-1)
Time (mins)
Pure Water Flux at 2 kg.cm-2 pressure
M0
M0.25
M0.5
17
with a maximum value of 99.25% for M0.5 membrane. The new membrane shows
increased dye rejection due to the additives and this can be attributed to 1) sieving
mechanism due to reduced pore size, 2) electrostatic repulsion due to the residual negative
charge on the membrane surface and 3) adsorption of the dye on the membrane surface. As
observed, increase in PANI-nanofibers lead to increase in all of the above three rejection
mechanisms mentioned above and result in increased dye rejection by the new membrane.
During the course of dye filtration, fouling is unavoidable [7] and hence the
membrane flux reduces over a period of time. The decrease in flux may be attributed to dye
adsorption on the membrane surface and pores. To evaluate the cleaning effectiveness and the
ability of the membrane to recover flux after being fouled, it is subjected to cleaning with
distilled water at increased pressure of 4 bar for 10 minutes and afterwards the pure water
flux at 2 bar was again measured. Flux recovery ratio (FRR), which is a measure of the
antifouling property of the membrane, was calculated and reported in Fig.11. From the
graphs, it is clear that increasing PANI-nanofiber concentration resulted in better flux
recovery ratio. The presence of PANI-nanofibers on the surface skin layer results in increased
hydrophilicity of the membrane, which may be responsible for the increased antifouling
ability of the membrane. Hydrophilic surface may not be easily adsorbed by the dye
molecules and thereby improves the antifouling property [36]. Thus we can conclude that the
addition of PANI-nanofibers imparts the better antifouling ability to the membranes.
96
96.5
97
97.5
98
98.5
99
99.5
100
20 30 40 50 60
Rej
ecti
on
, R
(%
)
Time, t (mins)
Dye Rejection at 2kg.cm-2 pressure
M0
M0.25
M0.5
18
Fig.10: Performance of PSf/PVP/PANI-nanofiber membrane for rejection of RR120 dye.
Fig.11: Flux Recovery Ratio of PSf/PVP/PANI nanofiber membrane for RR120 dye.
4. Conclusions
The effects of PANI-nanofibers on the hollow fiber membrane structure and performance
were analysed and reported. Filtration experiments were conducted to assess the applicability
and performance of the membrane for rejection of RR120 hazardous dye from water. From
the results obtained, the following can be concluded.
1. PANI-nanofibers in the range of 60 – 80nm and length around 150 – 300 nm were
synthesized via. interfacial polymerization process by oxidation of aniline in acidic
medium.
2. Novel PSf/PVP/PANI-nanofiber nanocomposite ultrafiltration hollow fiber membranes
were prepared via dry-wet spinning technique. The novel membranes showed well
formed asymmetrical structure with dense top layers and porous sub-layer.
3. The addition of PANI-nanofibers has resulted in a membrane with interconnected finger
like porous structure and more hydrophilic surface. The addition of PVP has resulted in
micro pores within the membrane structure with increased permeability.
4. The contact angle of the membranes decreased with increasing PANI-nanofiber
concentration, indicating increased hydrophilicity of the new membranes. The new
membranes also display higher thermal resistance.
52
54
56
58
60
62
64
66
68
70
M0 M0.25 M0.5 Flu
x R
ecover
y R
ati
o, F
RR
(%
)
Membranes
Flux Recovery
19
5. The PWF and rejection studies indicated improvement in membrane flux and dye
rejection with increasing PANI-nanofiber concentration.The best results were obtained
for M0.5 membrane with maximum rejection 99.25% at 2 bar for RR120 dye.
6. The new membranes have increased antifouling property due to the addition of PANI-
nanofibers.
Acknowledgements
We thank The Director, NITK, Surathkal, India for supporting research work and providing
financial assistance for travelling to Malaysia. We also thank members of Advanced
Membrane TEchnology Research Centre (AMTEC), Universiti Teknologi Malaysia, 81310
UTM, Skudai, Johor, Malaysia for their help.
References
[1] V.K. Gupta, R. Kumar, A. Nayak, T.A. Saleh, M. Barakat, Adsorptive removal of dyes
from aqueous solution onto carbon nanotubes: A review, Adv. Colloid Interface Sci., 193
(2013) 24-34.
[2] M.T. Yagub, T.K. Sen, S. Afroze, H. Ang, Dye and its removal from aqueous solution by
adsorption: A review, Adv. Colloid Interface Sci., 209 (2014) 172-184.
[3] M. Rafatullah, O. Sulaiman, R. Hashim, A. Ahmad, Adsorption of methylene blue on
low-cost adsorbents: a review, J. Hazard. Mater., 177 (2010) 70-80.
[4] A.K. Verma, R.R. Dash, P. Bhunia, A review on chemical coagulation/flocculation
technologies for removal of colour from textile wastewaters, J. Environ. Manage, 93 (2012)
154-168.
[5] P.V. Nidheesh, R. Gandhimathi, S.T. Ramesh, Degradation of dyes from aqueous solution
by Fenton processes: a review, Environ. Sci. Pollut. Res, 20 (2013) 2099-2132.
[6] F. Zhang, A. Yediler, X. Liang, A. Kettrup, Effects of dye additives on the ozonation
process and oxidation by-products: a comparative study using hydrolyzed CI< i> Reactive
Red 120</i>, Dyes Pigm., 60 (2004) 1-7.
[7] Y.K. Ong, F.Y. Li, S.-P. Sun, B.-W. Zhao, C.-Z. Liang, T.-S. Chung, Nanofiltration
hollow fiber membranes for textile wastewater treatment: Lab-scale and pilot-scale studies,
Chem. Eng. Sci., 114 (2014) 51-57.
[8] S. Yu, Z. Chen, Q. Cheng, Z. Lü, M. Liu, C. Gao, Application of thin-film composite
hollow fiber membrane to submerged nanofiltration of anionic dye aqueous solutions, Sep.
Purif. Technol., 88 (2012) 121-129.
20
[9] X. Wei, X. Kong, C. Sun, J. Chen, Characterization and application of a thin-film
composite nanofiltration hollow fiber membrane for dye desalination and concentration,
Chem. Eng. J. (Lausanne), 223 (2013) 172-182.
[10] Y. Zheng, G. Yao, Q. Cheng, S. Yu, M. Liu, C. Gao, Positively charged thin-film
composite hollow fiber nanofiltration membrane for the removal of cationic dyes through
submerged filtration, Desalination, 328 (2013) 42-50.
[11] S. Maurya, K. Parashuram, P. Singh, P. Ray, A. Reddy, Preparation of polysulfone–
polyamide thin film composite hollow fiber nanofiltration membranes and their performance
in the treatment of aqueous dye solutions, Desalination, 304 (2012) 11-19.
[12] M.D. Afonso, R. Bórquez, Review of the treatment of seafood processing wastewaters
and recovery of proteins therein by membrane separation processes—prospects of the
ultrafiltration of wastewaters from the fish meal industry, Desalination, 142 (2002) 29-45.
[13] N. Hamid, A.F. Ismail, T. Matsuura, A. Zularisam, W. Lau, E. Yuliwati, M. Abdullah,
Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO<
sub> 2</sub>) ultrafiltration membranes for humic acid removal, Desalination, 273 (2011)
85-92.
[14] E. Yuliwati, A.F. Ismail, T. Matsuura, M.A. Kassim, M. Abdullah, Effect of modified
PVDF hollow fiber submerged ultrafiltration membrane for refinery wastewater treatment,
Desalination, 283 (2011) 214-220.
[15] Allègre, C., Moulin, P., Maisseu, M., Charbit, F., “Treatment and reuse of reactive
dyeing effluents”, Journal of Membrane Science, 269 (2006), 15-34.
[16] Allègre, C., Moulin, P., Maisseu, M., Charbit, F., “Savings and re-use of salts and water
present in dye house effluents”, Desalination, 162 (2004), 13-22.
[17] Ranganathan, K., Karunagaran, K., Sharma, D.C., “Recycling of wastewaters of textile
dyeing industries using advanced treatment technology and cost analysis – Case studies”,
Resources, Conservation and Recycling, 50 (2007), 3, 306-318.
[18] Reife, A., Freeman, H.S., “Environmental Chemistry of Dyes and Pigments”, John
Wiley & Sons, (1996).
[19] Brandon, C.A., “Closed Cycle Textile Dyeing: Full-scale Hyperfiltration Demonstration,
Demonstration (Design), U.S. Environmental Protection Agency, EPA-600/2-80-005, March
1980.
[20] S.R. Panda, S. De, Preparation, characterization and performance of ZnCl< sub>
2</sub> incorporated polysulfone (PSF)/polyethylene glycol (PEG) blend low pressure
nanofiltration membranes, Desalination, 347 (2014) 52-65.
21
[21] R. Kumar, A.M. Isloor, A. Ismail, T. Matsuura, Performance improvement of
polysulfone ultrafiltration membrane using N-succinyl chitosan as additive, Desalination, 318
(2013) 1-8.
[22] R. Kumar, A.M. Isloor, A.F. Ismail, T. Matsuura, Synthesis and characterization of
novel water soluble derivative of Chitosan as an additive for polysulfone ultrafiltration
membrane, J. Membr. Sci., 440 (2013) 140-147.
[23] M. Padaki, A.M. Isloor, R. Kumar, A. Fauzi Ismail, T. Matsuura, Synthesis,
characterization and desalination study of composite NF membranes of novel Poly[(4-
aminophenyl)sulfonyl]butanediamide (PASB) and methyalated Poly[(4-
aminophenyl)sulfonyl]butanediamide (mPASB) with Polysulfone (PSf), J. Membr. Sci., 428
(2013) 489-497.
[24] R. Kumar, A.M. Isloor, A.F. Ismail, S.A. Rashid, A.A. Ahmed, Permeation, antifouling
and desalination performance of TiO2 nanotube incorporated PSf/CS blend membranes,
Desalination, 316 (2013) 76-84.
[25] X. Qu, P.J. Alvarez, Q. Li, Applications of nanotechnology in water and wastewater
treatment, Water Res., 47 (2013) 3931-3946.
[26] Razmjou, A., Resosudarmo, A., Holmes, R.L., Li, H., Mansouri, J., Chen, V., “The
effect of modified TiO2 nanoparticles on the polyethersulfone ultrafiltration hollow fiber
membranes”, Desalination, 287 (2012), 271-280.
[27] Jeong, B., Hoek, E.M.V., Yan, Y., Subramani, A., Huang, X., Hurwitz, G., Ghosh, A.K.,
Jawor, A., “Interfacial polymerization of thin film nanocomposites: A new concept for
reverse osmosis membranes”, Journal of Membrane Science, 294 (2007), 1-7.
[28] S. Bhadra, D. Khastgir, N.K. Singha, J.H. Lee, Progress in preparation, processing and
applications of polyaniline, Prog. Polym. Sci., 34 (2009) 783-810.
[29] Huang, J., “Synthesis and applications of conducting polymer polyanlinenanofibers”,
Pure and Applied Chemistry, 78 (2006), 15-27.
[30] Z. Fan, Z. Wang, N. Sun, J. Wang, S. Wang, Performance improvement of polysulfone
ultrafiltration membrane by blending with polyaniline nanofibers, J. Membr. Sci., 320 (2008)
363-371.
[31] B. Chakrabarty, A. Ghoshal, M. Purkait, Preparation, characterization and performance
studies of polysulfone membranes using PVP as an additive, J. Membr. Sci., 315 (2008) 36-
47.
22
[32] C. Feng, K. Khulbe, T. Matsuura, A. Ismail, Recent progresses in polymeric hollow fiber
membrane preparation, characterization and applications, Sep. Purif. Technol., 111 (2013)
43-71.
[33] S. Xing, H. Zheng, G. Zhao, Preparation of polyaniline nanofibers via a novel interfacial
polymerization method, Synth. Met., 158 (2008) 59-63.
[34] C. Ong, W. Lau, P. Goh, B. Ng, A. Ismail, Preparation and characterization of PVDF–
PVP–TiO2 composite hollow fiber membranes for oily wastewater treatment using
submerged membrane system, Desalin. Water Treat, (2013) 1-11.
[35] A. Zulhairun, A. Ismail, T. Matsuura, M. Abdullah, A. Mustafa, Asymmetric mixed
matrix membrane incorporating organically modified clay particle for gas separation, Chem.
Eng. J. (Lausanne), 241 (2014) 495-503.
[36] S. Zhao, Z. Wang, X. Wei, X. Tian, J. Wang, S. Yang, S. Wang, Comparison study of
the effect of PVP and PANI nanofibers additives on membrane formation mechanism,
structure and performance, J. Membr. Sci., 385 (2011) 110-122.
[37] E. Alventosa-deLara, S. Barredo-Damas, E. Zuriaga-Agustí, M. Alcaina-Miranda, M.
Iborra-Clar, Ultrafiltration ceramic membrane performance during the treatment of model
solutions containing dye and salt, Sep. Purif. Technol., 129 (2014) 96-105.
[38] A. Rahimpour, S. Madaeni, A. Taheri, Y. Mansourpanah, Coupling TiO< sub> 2</sub>
nanoparticles with UV irradiation for modification of polyethersulfone ultrafiltration
membranes, J. Membr. Sci., 313 (2008) 158-169.
List of Contents
Fig.1: Molecular Structure of Reactive Red 120 dye.
Fig.2:(a) Schematic representation of the hollow fiber spinning set up, (b) cross-section of the
spinneret during spinning [32].
Fig.3: Self-Fabricated cross-flow filtration setup (a) Feed tank, (b) Diaphragm pump (c)
Bypass valve (d) Pressure Guage (e) Membrane module (f) Retentate Flow-control valve.
Fig.4: TEM images of PANI coated TiO2 nanotubes (A and B)
Fig.5:SEM images of PSf/PVP/PANI-nanofiber hollow fiber membrane cross-sections. (a,
A) Sample-00: M0, (b,B) Sample-01: M0.25, (c,C) Sample-02: M0.5.
Fig.6:Contact angle measurements of PSf/PVP/PANI-nanofiber hollow fiber membranes.
Fig.7: Zeta Potential measurements of PSf/PVP/PANI-nanofiber hollow fiber membranes.
Fig.8: DSC thermographs of PSf/PVP/PANI-nanofiber hollow fiber membranes.
23
Fig.9:PWF of PSf/PVP/PANI nanofiber hollow fiber membrane.
Fig.10:Performance of PSf/PVP/PANI-nanofiber membrane for rejection of RR120 dye.
Fig.11:Flux Recovery Ratio of PSf/PVP/PANI nanofiber membrane for RR120 dye.
List of Tables
Table1: Dope solutions for PSf/PVP/PANI Nanofiber hollow fiber membrane
Table 2: Spinning Parameters for PSf/PVP/PANI-nanofiber hollow fiber membranes
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